JP4178393B2 - Carrier detection method and terminal device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a carrier detection method in a burst signal transmission system.
[0002]
[Prior art]
In a burst signal transmission system such as a wireless LAN (Local Area Network) that employs a CSMA / CA (Carrier Sense Multiple Access Collision Aidance) method as a wireless access method, a base station is a terminal belonging to the base station at the same time. Only one terminal in the group can communicate. In such a system, a base station normally gives identification information to individual terminals when establishing a circuit for a group of terminals belonging to the base station. When the base station transmits a burst signal to one terminal in the terminal group belonging to the base station, identification information for the terminal is added to the head of the burst signal and transmitted. All terminals measure the received signal level for the burst signal transmitted from the base station, and compare the measured value with a preset determination threshold (hereinafter referred to as carrier detection threshold). When the measured value exceeds the carrier detection determination threshold, it is determined that the carrier has been detected, and the demodulation operation is started. On the other hand, if the measured value falls below the carrier detection threshold, it is determined that no carrier is detected, and the demodulation operation is stopped. These are expressed as follows.
[0003]
(Carrier detection condition)
RSSI ≧ Th_CS (1)
(Carrier non-detection condition)
RSSI <Th_CS (2).
[0004]
In equations (1) and (2), RSSI represents a measured value of received power at the receiver, and Th_CS represents a carrier detection threshold.
[0005]
By performing the above carrier detection, unnecessary demodulation operation is omitted when a carrier is not detected, so that the power consumption of the receiver can be reduced. Here, if the carrier detection threshold Th_CS is set high, the carrier detection probability decreases, so that the probability of not detecting a carrier increases even at a reception signal level that can be demodulated originally, and communication efficiency deteriorates. On the other hand, if the carrier detection determination threshold Th_CS is lowered, the probability of detecting reception noise power and interference power from other carriers increases, the probability of performing unnecessary carrier detection increases, and the receiver is unnecessary. Therefore, there is a problem that the effective power consumption of the battery is reduced due to an increase in power consumption. From the above, it is desirable to set an optimum value for the carrier detection threshold Th_CS in consideration of communication efficiency and power consumption.
[0006]
As a conventional technique related to a method for optimizing a determination threshold, there is a method in which an RSSI signal is held in advance in a state where no carrier is detected, and a carrier detection threshold Th_CS is adaptively set based on the RSSI signal ( Patent Document 1). A terminal that satisfies Equation (1) and is determined to detect a carrier starts demodulation processing of the received signal, and whether or not the burst signal is addressed to itself based on terminal identification information added to the head of the burst signal. Determine. If it is addressed to itself, the data demodulation operation after the burst signal identification information is continued, and if it is not addressed to itself, the data demodulation operation after the burst signal identification information is stopped.
[0007]
[Patent Document 1]
JP 2000-156666 A
[Problems to be solved by the invention]
In the above prior art, even when the terminal receives only the interference signal, when the RSSI satisfies Expression (1), the demodulation operation up to the terminal identification information of the burst signal is performed. Therefore, there is a problem that power consumption increases due to unnecessary operation of the demodulation circuit, and the effective time of the battery is reduced. In addition, an unnecessary increase in the processing time of the demodulation circuit has a problem of reducing the communication efficiency of the system.
[0009]
An object of the present invention is to provide a carrier detection method in which a demodulation operation is not performed when a terminal receives only an interference signal even if a measured value of received power at a receiver exceeds a carrier detection threshold. It is in.
[0010]
In order to achieve the above object, the present invention starts demodulation of a received signal when a received signal having a magnitude exceeding a predetermined threshold is detected. If the received signal is not within a predetermined range, the demodulation is performed. In the carrier detection method to be stopped, the magnitude and arrival probability of the received signal that has not been demodulated are reflected in the determination of the predetermined range .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
Referring to FIG. 1, a block diagram of a burst signal transmission system according to an embodiment of the present invention is shown. The terminal 20 and the terminal 21 belong to the base station 10 configuring the cell 30. The individual information burst signals transmitted from the base station 10 to the terminals 20 and 21 are referred to as an individual information burst signal 40 and an individual information burst signal 41, respectively.
[0014]
Hereinafter, the demodulation operation of the terminal 20 and the terminal 21 with respect to the individual information burst signal will be described. As an example, consider a case where the base station 10 transmits an individual information burst signal 40 to the terminal 20. In this case, the demodulation of the individual information burst signal 40 in the terminal 20 and the terminal 21 begins with the demodulation operation of the terminal 20 and the terminal 21 when the RSSI for the individual information burst signal 40 satisfies Equation (1). The terminal identification information added to the head of the individual information burst signal identifies which terminal the individual information burst signal is addressed to. In the above example, since the individual information burst signal 40 is addressed to the terminal 20, the terminal 20 demodulates data after the terminal identification information with respect to the individual information burst signal 40. On the other hand, since the individual information burst signal 40 is not addressed to the terminal 21, the terminal 21 does not demodulate data after the terminal identification information.
[0015]
On the other hand, in the burst signal transmission system of this embodiment, the base station 10 transmits the broadcast information burst signal 50 at regular time intervals. Since the broadcast information burst signal 50 is broadcast to the terminals 20 and 21 belonging to the base station 10, the terminals 20 and 21 demodulate the broadcast information burst signal 50. Demodulation of the broadcast information burst signal 50 at the terminal 20 and the terminal 21 starts the demodulation operation when the RSSI for the broadcast information burst signal 50 satisfies the equation (1), and is placed at the head of the broadcast information burst signal 50. Based on the added terminal identification information, it is determined that it is a broadcast information burst signal, and both the terminal 20 and the terminal 21 demodulate data after the terminal identification information added to the head of the broadcast information burst signal 50.
[0016]
Next, the basic concept of the carrier detection method at the terminal for the burst signal transmission system of the present embodiment will be described.
[0017]
First, the terminal holds the RSSI at the time when the expression (1) is satisfied, and sets the held RSSI as RSSI_sta. Then, from the terminal identification information of the individual information burst signal and the broadcast information burst signal, it is determined whether or not the received burst signal is a signal from the base station to which the terminal belongs, and the terminal belongs to In the case of a signal from the base station, based on the information in which RSSI_sta is set from the retained RSSI, the terminal determines the RSSI range for determining the start / stop of the demodulation operation of the burst signal received next time as Set to.
[0018]
RSSI_sta-Th_win / 2 <RSSI <RSSI_sta + Th_win / 2 (3).
[0019]
Here, Th_win is a setting value that determines the RSSI range. In addition, the relationship between Th_CS in Expression (1) and Expression (2) and RSSI_sta and Th_win in Expression (3) shall satisfy the following expression.
[0020]
Th_CS <RSSI_sta-Th_win / 2 <RSSI_sta <RSSI_sta + Th_win / 2 (4).
[0021]
The terminal starts the demodulation operation when the received RSSI satisfies Equation (3), and stops the demodulation operation when it does not satisfy Equation (3). The basis of this embodiment is to determine the start or stop of the demodulating operation of the received burst signal by determining whether or not the RSSI of the received signal is within the range indicated by Equation (3). is there.
[0022]
Referring to FIG. 2, a flowchart showing a processing flow of the carrier detection method of the present embodiment is shown.
[0023]
In step 100, a communication line is established between the terminal and the base station. Assume that the initial values of RSSI_sta and Th_win in Equation (3) are set at the time of line establishment.
[0024]
In step 101, the terminal measures RSSI. In step 102, it is determined whether the RSSI satisfies the conditional expression (1). If the RSSI satisfies the conditional expression (1), it is determined in step 103 that a carrier has been detected, and the RSSI measured in step 101 is held. If the RSSI does not satisfy the conditional expression (1), it is determined that no carrier is detected, and the process returns to step 101.
[0025]
In step 130, the terminal determines the condition of equation (3). If the RSSI held in step 101 satisfies the condition of equation (3), the demodulation operation is started in step 120. If the condition of equation (3) is not satisfied, the demodulation operation is stopped in step 121. Return to 101.
[0026]
After step 120, in step 104, it is determined from the terminal identification information of the burst signal obtained by demodulation whether or not the received burst signal is transmitted from the base station to which the terminal belongs. If it is determined that the burst signal received in step 104 is not transmitted from the base station to which the terminal belongs, the demodulation operation is stopped in step 123 and the process returns to step 101. If it is determined that the burst signal received in step 104 is transmitted from the base station to which the terminal belongs, in step 105, RSSI_sta in equation (3) is updated using the RSSI held in step 103.
[0027]
The setting of RSSI_sta in step 105 may improve the setting accuracy of RSSI_sta by, for example, performing weighted averaging of past RSSI_sta using a weighting filter having a transfer function represented by the following equation.
[0028]
RSSI_sta. avg (n) = W × RSSI_sta. avg (n-1) + (1-W) * RSSI_sta (n) (5).
[0029]
Here, RSSI_sta. avg (n) and RSSI_sta (n) represent the output and input of the weighting filter at time n, respectively. W is a weighting coefficient that ranges from 0 to 1. When the weighting filter represented by Expression (5) is used, RSSI_sta. avg (n) corresponds to RSSI_sta in equation (3) at time n.
[0030]
After step 105, in step 106, it is determined whether or not the broadcast information burst signal transmitted from the base station at regular time intervals can be received with a high probability. If the signal can be received with a probability equal to or greater than step 106, Th_win in equation (3) is reduced in step 107, and if not received with a certain probability or more, Th_win in equation (3) is determined in step 108. Enlarge.
[0031]
After the processing of step 107 or step 108 is completed, the process returns to step 101. The process shown in FIG. 2 is performed until the terminal cancels the line establishment.
[0032]
Next, the configuration of a terminal that implements the carrier detection method of this embodiment will be described.
[0033]
Referring to FIG. 3, the configuration of the receiving unit of the terminal according to this embodiment is shown. A terminal extracts a signal in a band used for communication by the reception filter 300 from a signal (reception signal) received by an antenna. The RSSI measurement unit 301 receives the output of the reception filter 300 and calculates a reception signal level (RSSI). The carrier detection unit A302 determines whether or not the condition of the expression (1) is satisfied with respect to the RSSI calculated by the RSSI measurement unit 301. When the expression (1) is satisfied, the measurement is performed by the RSSI measurement unit 301. The RSSI is notified to the RSSI_sta calculation unit 304, and the demodulation unit 303 is notified of the start of the demodulation operation. On the other hand, if the carrier detection unit A302 does not satisfy the condition of the expression (1), the demodulation unit 303 is notified of the stop of the demodulation operation. The demodulator 303 performs data demodulation of the received signal.
[0034]
Based on the base station information demodulated by the demodulation unit 303, the base station information identification unit 305 determines whether or not the base station that has transmitted the signal received by the terminal is the base station to which the terminal belongs. If the base station that transmitted the signal received by the terminal is the base station to which the terminal belongs, the base station information identifying unit 305 notifies the RSSI_sta calculation unit 304, and the base station that transmitted the signal received by the terminal If it is not the base station to which the terminal belongs, the demodulation section 303 is notified of the stop of the demodulation operation. When the RSSI_sta calculation unit 304 receives a notification from the base station information identification unit 305 that the base station that has transmitted the signal received by the terminal is the base station to which the terminal belongs, the RSSI measurement used in the carrier detection unit A302 Using RSSI in unit 301, RSSI_sta in equation (3) is calculated / updated.
[0035]
The window setting unit 306 receives the broadcast information burst signal received from the base station to which the terminal belongs from the base station information identifying unit 305, and uses the information to set Th_win shown in Equation (3). At the same time, the RSSI_sta value is received from the RSSI_sta calculation unit 304, and the RSSI range represented by Expression (3) is set.
[0036]
In the carrier detection unit B307, the RSSI measurement value is received from the RSSI measurement unit 301, and it is determined whether or not the RSSI measurement value satisfies Expression (3). In the carrier detection unit B307, when the RSSI measurement value received from the RSSI measurement unit 301 satisfies the equation (3), the demodulation unit 303 is notified of the start of the demodulation operation, and when the equation (3) is not satisfied, The demodulation unit 303 is notified of the stop of the demodulation operation.
[0037]
The fundamental part of the present embodiment is to determine the start or stop of the demodulation operation of the received burst signal by setting the RSSI range represented by Expression (3).
[0038]
Next, the operation of the present embodiment will be described with reference to FIG.
[0039]
FIG. 4 shows a general relationship between the logarithmic value (Log display) of the distance R between the terminal and the base station to which the terminal belongs and the RSSI. FIG. 4 shows that the relationship between the distance R between the terminal and the base station and the RSSI has a one-to-one relationship, and the RSSI decreases as the distance R between the terminal and the base station increases.
[0040]
As an example, consider the case where Log (R) = Rx, and the RSSI at this time is RSSI_x. In this case, it can be said that the greater the error between the RSSI and RSSI_x actually received by the terminal (the error Er in FIG. 4), the higher the possibility that the signal is not received from the base station. In other words, the probability that the measured RSSI is receiving an interference signal coming from other than the base station to which the terminal belongs increases. Since the interference signal becomes a communication interference signal for the terminal, the terminal receiving the interference signal is forced to perform an unnecessary demodulation operation. Therefore, if the probability that a terminal receives an interference signal increases, the probability that the terminal performs an unnecessary demodulation operation increases.
[0041]
In the present embodiment, the RSSI_sta in the equation (3) is calculated to estimate the RSSI_x, and the allowable error is set by Th_win in the equation (3). By stopping the demodulation operation, there is an effect of reducing the probability of causing the terminal to perform an unnecessary demodulation operation as described above. In addition, the RSSI_sta setting in Equation (3) is adaptively averaged based on past information to improve the RSSI_sta estimation accuracy, thereby further reducing the probability of causing the terminal to perform unnecessary demodulation operations. There is. In addition, when Th_win in Expression (3) is adaptively variable according to the reception success probability of the broadcast information burst signal, when the probability of receiving the reception signal from the base station is high, Expression (3) If the probability of receiving interference power is reduced by narrowing the RSSI range in, and the probability of receiving a received signal from the base station is low, the received signal from the base station is expanded by expanding the RSSI range in Equation (3). There is an effect of improving the communication efficiency by reducing the probability of not receiving. Further, adaptively controlling RSSI_sta and Th_win in Equation (3) has an effect of enabling control independent of a propagation model between a terminal and a base station belonging to the terminal.
[0042]
【The invention's effect】
As described above, according to the present invention, compared with the carrier detection method using only the equation (1) in the prior art, the probability of reducing unnecessary demodulation operation when the terminal receives an interference signal is reduced. Since it can be increased, there is an effect of reducing the power consumption of the terminal and improving the communication efficiency. Also, by adaptively controlling RSSI_sta and Th_win in equation (3), autonomous control independent of the propagation model between the terminal and the base station to which the terminal belongs can be performed. Compared with the case where is fixed, there is an effect of reducing the man-hour for the optimum design of the set value.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a burst signal transmission system according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a processing flow of a carrier detection method of the present embodiment.
FIG. 3 is a diagram illustrating a receiver configuration of a terminal according to the present embodiment.
FIG. 4 shows a general relationship between a logarithmic value (Log) of a distance R between a terminal and a base station to which the terminal belongs, and RSSI.
[Explanation of symbols]
10 Base station 20, 21 Terminal 30 Cell 40, 41 Individual information burst signal 50 Broadcast information burst signal 60, 61 Interference signal 101-123 Step 300 Reception filter 301 RSSI measurement unit 302 Carrier detection unit A
303 Demodulator 304 RSSI_sta Calculation Unit 305 Base Station Information Detection Unit 306 Window Setting Unit 307 Carrier Detection Unit B

Claims (2)

In a carrier detection method in which when a received signal having a magnitude exceeding a predetermined threshold is detected, demodulation of the received signal is started, and if the magnitude of the received signal is not within a predetermined range, the demodulation is stopped .
A carrier detection method characterized by reflecting the magnitude and arrival probability of a received signal whose demodulation is not stopped in the determination of the predetermined range . A terminal having means for starting demodulation of the received signal when a received signal having a magnitude exceeding a predetermined threshold is detected; and means for stopping the demodulation if the magnitude of the received signal is not within a predetermined range In the device
The terminal device further comprising means for reflecting the magnitude and arrival probability of the received signal that has not been demodulated to the determination of the predetermined range .

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